Gas sensing element employable in an exhaust system of an internal combustion engine

A gas sensing element comprising:

• first and second chambers into which an objective gas to be measured is introduced;
• a first diffusion resistive passage connecting said first chamber to an outside of said gas sensing element;
• a second diffusion resistive passage connecting said first chamber to said second chamber;
• a pump cell provided on a surface defining said first chamber for pumping oxygen in accordance with an applied voltage;
• a first monitor cell provided on a surface defining said first chamber for generating an electromotive force representing an oxygen concentration in said first chamber;
• a second monitor cell provided on a surface defining said second chamber for generating an electromotive force representing an oxygen concentration in said second chamber;
• and
• a sensor cell provided on a surface defining said second chamber and responsive to application of a predetermined voltage for generating a sensor current representing a specific gas concentration in said objective gas,
• wherein said voltage applied to said pump cell is controlled based on a difference between the electromotive forces obtained from said first and second monitor cells.